Devices have been used to drop balls or plugs into the wellbore, generally as part of a cementing process for a liner or casing. Balls can be dropped to actuate external packers or liner hangers, while wiper plugs are dropped during the cementing process, with one of the major purposes to wipe the cement from the casing or liner. In this patent application, reference will be made to plug-dropping head with the understanding that different types of objects can be dropped or inserted through it and the reference to plug-dropping head is meant for convenience to be all-inclusive. In situations that required multiple drops of plugs, plug-dropping heads in the past have been stacked vertically, one on top of the other, such that the assemblies could grow to a dimension of nearly 20 ft. or more. Typical of such devices is one made by Nodeco, designated as a top-drive cementing head for dual darts. This assembly is indicated as being approximately 2400 mm long. Other companies have made plug-dropping heads to drop multiple plugs and, in general, all these prior designs have vertically stacked similar or identical assemblies on top of each other so that plugs are arranged one on top of the next and can be dropped sequentially, starting with the lowermost plug. Since these plug-dropping heads are frequently inaccessible to the rig floor, devices have been developed to remotely actuate these plug-dropping heads so that one or more plugs can be dropped when desired. Patents which illustrate the remote actuation of plug-dropping heads are U.S. Pat. Nos. 5,435,390 and 5,590,713. These patents also incorporate the use of vertical stacking of plugs.
The problem with the prior art designs is that the assemblies were overly long, expensive to build, and time-consuming to assemble and effectively operate, primarily due to inaccessibility. What is needed is a compact device which could be simply operated which would also allow for dropping multiple plugs and/or balls. One of the objectives of the present invention is to provide such a compact design which could hold a multiplicity of plugs and/or balls in discrete chambers in a cylinder rotating about a vertical axis. Thus, the objective of a compact design is achieved with the present invention in view of its configuration. Another objective of the present invention is to provide an indexing feature which assures the desired alignment for dropping the plugs. Another objective of the present invention is to signal visually to rig personnel that a plug or ball or other object has been dropped. Yet another object is to allow actuation of the device with ongoing circulation and to configure the device in such a manner that circulation continues as the device is actuated. Yet another object is to construct the device in the manner so as to transmit torque therethrough without stressing threaded connections. Yet another objective is to provide a simple design which is not only compact but also reliable in operation. Those and other objectives of the present invention will become more apparent to those of skill in the art from a review of the preferred embodiment which is described below.